The present disclosure relates to toner transportation devices used in image forming apparatuses such as copiers, printers, facsimile machines, and multi-function machines that perform the functions of these devices.
In typical electrophotographic image forming apparatuses, an electrostatic latent image formed on an image carrying body such as a photoconductor drum is visualized by the developing device, typically using a powdery developer. The visualized image (toner image) is transferred to a recording medium and then fixed. Toner remaining on the surface of the image carrying body is removed by a cleaning device so as to form a new toner image. The residual toner removed by the cleaning device is stored in a waste toner bottle. When the waste toner bottle becomes full after a specified number of sheets have been printed, the user is notified of the full state, and the waste toner bottle is replaced and discarded.
A known toner transportation device uses a toner transportation path equipped with a transportation screw located in a pipe-shaped transportation path as a waste toner collection path from a cleaning device to a waste toner bottle. In such a toner transportation path, the locus of an outer circumferential edge of the transportation screw formed while the transportation screw is being rotated may become larger than the inner diameter of the transportation path due to, for example, a dimensional error in the outer diameter of the transportation screw or the inner diameter of the transportation path, or bowing of the transportation screw. In this situation, the transportation screw may not be able to rotate due to an excessive rotational load generated by friction. Thus, the outer diameter of the transportation screw is usually designed to be smaller than the inner diameter of the transportation path.
However, with such a design, there is a clearance (gap) formed between the transportation screw and the transportation path. Thus, when the transportation screw is bowed, the transportation screw swings in the radial directions (becomes eccentric) while being rotated. As a result, the transportation screw hits the inner surface of the transportation path and noise may be generated.
More specifically, when the transportation screw is bowed in a downwardly position, bending due to the weight of the transportation screw itself is added in the same direction as that of the bowing, thereby increasing the amount of deformation. In contrast, when the transportation screw is in an upwardly bowed position, bending due to the weight of the transportation screw itself acts in a direction opposite to the direction of the bowing, thereby decreasing the amount of bowing. Accordingly, when the transportation screw is rotated from the upwardly bowed position, the state of the transportation screw gradually changes from a balanced state, where the amount of deformation is small, into a state where bending due to the weight of the transportation screw increases the bowing. Thus, the transportation screw undergoes significant wave-like deformation while being rotated and hits the inner surface of the transportation path. At this time, noise generated due to the hitting becomes larger as the bowing is increased, the clearance (gap) between the transportation screw and the inner surface of the transportation path is increased, and the weight of the transportation screw is increased.
In view of the above-described situation, a proposed first exemplified toner transportation device has a portion, in which an outer edge of a spiral protrusion (spiral fin) of the transportation screw and an inner face of a cylindrical transportation path are in close proximity with each other. This allows the transportation screw to be stably rotated while part of the outer edge of the transportation screw is in contact with the inner face of the cylindrical transportation path.
A proposed second exemplified toner transportation pipe has a pipe main body having a semi-tubular portion and a semi-tubular lid body joined to the semi-tubular portion of the pipe main body. The plane where the pipe main body and the semi-tubular lid body are joined to each other is substantially flat, and the pipe main body and the tubular lid body are joined to each other by ultrasonic welding so that the toner transportation pipe has good air tightness and dimensional accuracy.
Furthermore, in a proposed third exemplified developer transportation device, a bearing that receives a shaft end portion of a transportation screw has a space so as to allow a developer to pass through the space. Thus, the developer can be smoothly transported while vibration due to rotation of the transportation screw is suppressed.
However, in the first and second examples, there is a limit in setting the clearance between the transportation screw and the cylindrical transportation path due to the dimensional tolerance of component and the assembly tolerance. When bowing of the transportation screw exceeds the clearance, the transportation screw hits the inner surface of the transportation path. Thus, the noise due to the hitting is not necessarily reliably prevented. In the first example, the portion, in which the outer diameter of the spiral fin and the inner diameter of the cylindrical transportation path are in proximity with each other, is formed over the entire periphery at a portion in the axial direction of the cylindrical transportation path. Thus, toner tends to clog the transportation path, thereby increasing the rotational load of the transportation screw. As a result, the fluidity of the toner is decreased by frictional heat, and accordingly, transportation efficiency is degraded. When the toner is left in this state for a long time, there is a possibility of the toner being caked.
With the structure of the third example, since the bearing allows the developer to pass therethrough, vibration at the end portion of the transportation screw can be suppressed. However, it is thought that the above-described deformation of the central portion of the transportation screw caused by bowing of the transportation screw and bending due to the weight of the transportation screw cannot be suppressed. Also in the third example, the bearing has an annular shape, the outer circumferential surface of which is fitted into the developer transportation path and the inner circumferential surface of which slides against a rotational shaft of the transportation screw. Thus, there is a possibility of the entire periphery of the rotational shaft rubbing against the inner circumferential surface of the bearing, thereby increasing the rotational load.
In the above-described situations, the toner transportation path equipped with the transportation screw in the pipe-shaped transportation path is used for the waste toner transportation path from the cleaning device to the waste toner bottle. However, use of the toner transportation path equipped with the transportation screw in the pipe-shaped transportation path is not limited to the waste toner transportation path. In image forming apparatuses, a toner cartridge is provided in order for a developing device to be replenished with toner. A similar situation is also observed in the situation where the toner transportation path equipped with the transportation screw in the transportation pipe is used in a toner replenishment path, which is used when the developing device is replenished with toner from a toner cartridge in accordance with the consumption of toner in the developing device.